<template>
  <div class="countTo">
    {{ state.displayValue }}
  </div>
</template>

<script setup>
// vue3.2新的语法糖, 编写代码更加简洁高效
import { onMounted, onUnmounted, reactive } from "@vue/runtime-core";
import { watch, computed } from "vue";
import {
  requestAnimationFrame,
  cancelAnimationFrame,
} from "./requestAnimationFrame.js";
// 定义父组件传递的参数
const props = defineProps({
  start: {
    type: Number,
    required: false,
    default: 0,
  },
  end: {
    type: Number,
    required: false,
    default: 2021,
  },
  duration: {
    type: Number,
    required: false,
    default: 5000,
  },
  autoPlay: {
    type: Boolean,
    required: false,
    default: true,
  },
  decimals: {
    type: Number,
    required: false,
    default: 0,
    validator(value) {
      return value >= 0;
    },
  },
  decimal: {
    type: String,
    required: false,
    default: ".",
  },
  separator: {
    type: String,
    required: false,
    default: ",",
  },
  prefix: {
    type: String,
    required: false,
    default: "",
  },
  suffix: {
    type: String,
    required: false,
    default: "",
  },
  useEasing: {
    type: Boolean,
    required: false,
    default: true,
  },
  easingFn: {
    type: Function,
    default(t, b, c, d) {
      return (c * (-Math.pow(2, (-10 * t) / d) + 1) * 1024) / 1023 + b;
    },
  },
});

const isNumber = (val) => {
  return !isNaN(parseFloat(val));
};

// 格式化数据，返回想要展示的数据格式
const formatNumber = (val) => {
  val = val.toFixed(props.default);
  val += "";
  const x = val.split(".");
  let x1 = x[0];
  const x2 = x.length > 1 ? props.decimal + x[1] : "";
  const rgx = /(\d+)(\d{3})/;
  if (props.separator && !isNumber(props.separator)) {
    while (rgx.test(x1)) {
      x1 = x1.replace(rgx, "$1" + props.separator + "$2");
    }
  }
  return props.prefix + x1 + x2 + props.suffix;
};

// 相当于vue2中的data中所定义的变量部分
const state = reactive({
  localStart: props.start,
  displayValue: formatNumber(props.start),
  printVal: null,
  paused: false,
  localDuration: props.duration,
  startTime: null,
  timestamp: null,
  remaining: null,
  rAF: null,
});

// 定义一个计算属性，当开始数字大于结束数字时返回true
const stopCount = computed(() => {
  return props.start > props.end;
});
// 定义父组件的自定义事件，子组件以触发父组件的自定义事件
const emits = defineEmits(["onMountedcallback", "callback"]);

const startCount = () => {
  state.localStart = props.start;
  state.startTime = null;
  state.localDuration = props.duration;
  state.paused = false;
  state.rAF = requestAnimationFrame(count);
};

watch(
  () => props.start,
  () => {
    if (props.autoPlay) {
      startCount();
    }
  }
);

watch(
  () => props.end,
  () => {
    if (props.autoPlay) {
      startCount();
    }
  }
);
// dom挂在完成后执行一些操作
onMounted(() => {
  if (props.autoPlay) {
    startCount();
  }
  emits("onMountedcallback");
});
// 暂停计数
const pause = () => {
  cancelAnimationFrame(state.rAF);
};
// 恢复计数
const resume = () => {
  state.startTime = null;
  state.localDuration = +state.remaining;
  state.localStart = +state.printVal;
  requestAnimationFrame(count);
};

const pauseResume = () => {
  if (state.paused) {
    resume();
    state.paused = false;
  } else {
    pause();
    state.paused = true;
  }
};

const reset = () => {
  state.startTime = null;
  cancelAnimationFrame(state.rAF);
  state.displayValue = formatNumber(props.start);
};

const count = (timestamp) => {
  if (!state.startTime) state.startTime = timestamp;
  state.timestamp = timestamp;
  const progress = timestamp - state.startTime;
  state.remaining = state.localDuration - progress;
  // 是否使用速度变化曲线
  if (props.useEasing) {
    if (stopCount.value) {
      state.printVal =
        state.localStart -
        props.easingFn(
          progress,
          0,
          state.localStart - props.end,
          state.localDuration
        );
    } else {
      state.printVal = props.easingFn(
        progress,
        state.localStart,
        props.end - state.localStart,
        state.localDuration
      );
    }
  } else {
    if (stopCount.value) {
      state.printVal =
        state.localStart -
        (state.localStart - props.end) * (progress / state.localDuration);
    } else {
      state.printVal =
        state.localStart +
        (props.end - state.localStart) * (progress / state.localDuration);
    }
  }
  if (stopCount.value) {
    state.printVal = state.printVal < props.end ? props.end : state.printVal;
  } else {
    state.printVal = state.printVal > props.end ? props.end : state.printVal;
  }

  state.displayValue = formatNumber(state.printVal);
  if (progress < state.localDuration) {
    state.rAF = requestAnimationFrame(count);
  } else {
    emits("callback");
  }
};
// 组件销毁时取消动画
onUnmounted(() => {
  cancelAnimationFrame(state.rAF);
});
</script>
<style scoped>
.countTo{
  display: inline-block;
}
</style>
